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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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,     COLUMBIA GLACIER                                        277
and how much between 1905 and 1909, nor how much should be added for readvance after continuation of the retreat that was in progress in 1899. Between August, 1909, and July, 1910, there was additional advance here of about 165 feet, followed by additional advance from July to September, 1910. As the advance on the western margin is at least 1700 feet an advance of over 1600 feet near the middle of the glacier during this decade is not abnormal. It suggests, of course, that there was similar greater retreat and readvance on the north of islet Heather Island and that the table based on Grant's measurements, should be amplified as follows:
Date of Observation
Nature of Change
Unknown date to 1892 (probably).....
1892 (probably) to July 25-7, 1899.. ..
July 25-7, 1899, to unknown date.....
Unknown date to second unknown date Second unknown date to July 10, 1905. July 10, 1905, to third unknown date . . Third unknown date to July 15, 1908 ..
July 15, 1908, to June 24, 1909.......
June 24, 1909, to August 23, 1909.....
August 28, 1909, to July 4, 1910......
July 4, 1910, to September 5, 1910 ....
Advance
Retreat1
Retreat continued
Advance
Retreat
Retreat continued
Advance
Advance continued
Advance continued
Advance continued
Advance continued
The Eastern Ice Cliff. The eastern ice cliff of Columbia Glacier extends from the morainic islet in the cove, described above, northeastward to the mainland. It is a mile and a quarter in length, very sinuous, and rises approximately two hundred feet above the water in a pinnacled and crevassed cliff whose white or blue clearness is not obscured by morainic load except for certain black basal layers and a lateral moraine strip on the east near where the glacier reaches the mainland. This eastern cliff changed very decidedly from 1909 to 1910. In the former year it was almost exactly as in 1899, 1905, and 1908; evidently rising out of shallow water and resting on bottom, for, although the cliff was precipitous, there is no great activity of iceberg discharge. All the bergs were small, and all were apparently discharged by sliding down the ice front. Photographs taken from Gilbert's 1497 foot station (I), on the hillside to the east show that this part of the eastern ice cliff advanced slightly between 1899 and 1909.
In 1910 the ice cliff had advanced 150 or 200 feet more, pushing up a terminal moraine in front of it so that except in the western hah* mile no part of the eastern ice cliff ended in tidewater. Even the western portion did not reach the bay proper but ended in a cove, for the tidal cliff is fronted by the low barren islet previously alluded to. Here the water is evidently deep and small icebergs are occasionally discharged. The water in front of the eastern half of the cliff is shallow, being only 57 feet deep at a distance
* Perhaps interrupted by a slight readvance, about 1897 or 1898, suggested by the small inner push moraine observed by Gilbert in 1899 on the western shore of the bay, on the islet north of Heather Island, and on the mainland to the east. The fluted ground moraine beside Heather Island terminus also suggests an advance between 1892 and 1899, as Gflbert says (Op. tit, p. 78).